Unit 731 of the Japanese Imperial Army secretly developed and tested bacteriological weapons on human subjects in Manchuria during the Sino-Japanese War. At the end of the war, evidence was destroyed, and personnel kept silent, concealing the truth for decades. However, NHK recently found more than 20 hours of audio recordings from a 1949 war-crimes tribunal. The tapes contain former Unit 731 members' testimony about how, for example, typhoid and plague pathogens were tested on scores of Chinese and Manchurian prisoners. It is estimated that more than 3,000 people lost their lives after being used as living subjects. The human experiments were directed by medical scientists, who were recruited from more than 10 elite universities and research institutes. What was the nature of their experiments, and why did these doctors violate their commitment to preserving human life?